Mechanical patterning of a device layer

ABSTRACT

A method of fabricating a device, including mechanically patterning a device layer using a stamp containing a desired pattern. The device layer is formed on a plastic or polymeric substrate. The stamp is pressed against the substrate under a load which patterns the device layer without cracking the device layer in the non-patterned areas.

FIELD OF THE INVENTION

The present invention relates to the fabrication of devices. Moreparticularly, the invention relates to patterning of a device layer on asubstrate.

BACKGROUND OF THE INVENTION

In device fabrication, one or more device layers are formed on asubstrate. The layers are sequentially deposited and patterned to createfeatures on the surface of the substrate. The layers can be patternedindividually and/or as a combination of layers to form the desiredfeatures. The features serve as components that perform the desiredfunctions, creating the device.

One type of device which is of particular interest is a light emittingdiode (LED). Typically, an LED cell or pixel comprises one or morefunctional layers sandwiched between two electrodes to form a functionalstack. Charge carriers are injected from both electrodes. These chargecarriers recombine in the functional layer or layers, causing visibleradiation to emit. Recently, significant advances have been madeutilizing organic functional layers to form organic LEDs (OLEDs). Suchdevices are fabricated on rigid glass substrates having a thickness ofabout 0.3-1.1 mm.

Typically, OLED devices comprises a plurality of OLED pixels arranged toform a display, such as a flat panel display (FPD). A pixelated OLEDdevice includes, for example, a plurality of first electrode stripsformed on the substrate. The strips are arranged in a first direction.One of more organic layers are formed on the first electrodes strips. Aplurality of second electrode strips is formed over the organic layersin a second direction. Typically, the first and second electrode stripsare orthogonal to each other. The intersections of the first and secondelectrode strips form LED pixels.

The first electrode strips are created on the substrate by patterning anelectrode layer. Conventionally, the electrode layer is patterned byphotolithographic and etch processes. For example, a photosensitiveresist layer is deposited on the electrode. The resist layer is exposedwith radiation having the desired pattern defined by a mask. Afterdevelopment, unwanted resist is removed to expose portions of theelectrode beneath. The exposed portions are removed by a wet etch,leaving the desired pattern on the electrode layer. Thus, conventionaltechniques for patterning the electrode require numerous steps,increasing raw process time and manufacturing cost.

As evidenced by the above discussion, it is desirable to provide asimplified process of patterning a device layer.

SUMMARY OF THE INVENTION

The invention relates to patterning a device layer on a substrate duringdevice fabrication. In accordance with the invention, the patterning ofthe device layer an is achieved using a stamp with a pattern thereon.The pattern is formed by protrusions having a height greater than thethickness of the device layer to pattern the device layer. The stamp ispressed against the surface of the substrate under a load which patternsthe device layer. The load is selected to precisely control cracking theedges of the patterned areas but without cracking the non-patternedareas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic pixel LED;

FIGS. 2-4 show a process for patterning a device layer in accordancewith one embodiment of the invention; and

FIG. 5 shows an alternative process for patterning a device layer.

PREFERRED EMBODIMENTS OF THE INVENTION

The invention relates generally to the fabrication of devices. Inparticular, the invention describes a process for patterning a devicelayer on a substrate, particularly a device layer formed on a ductile orflexible substrate. Various types of devices can be formed by thepresent invention. For example, electrical, mechanical, orelectromechanical devices can be formed. Also, the invention can beuseful in fabricating a microelectromechanical system (MEMS). In oneembodiment, a process for forming a pixelated organic LED device isprovided.

FIG. 1 shows a cross-section of an OLED pixel. As shown, a substrate 101is provided. The substrate provides support for the LED pixel. Afunctional stack 105 comprising of one or more organic functional layers120 formed between conductive layers 110 and 150 is formed on thesubstrate, creating the LED pixel. The conductive layer 110 serves as ananode and the conductive layer 150 serves as a cathode.

A plurality of LED pixels can be arranged on the substrate to form anFPD. The FPD is used in various consumer electronic products, includingcellular phones, cellular smart phones, personal organizers, pagers,advertising panel, touch screen displays, teleconferencing equipment,multimedia equipment, virtual reality products, and display kiosks.

FIGS. 2-5 show a process for patterning a device layer on a substrate inthe fabrication of a device. In one embodiment, the device fabricatedcomprises a pixelated OLED device. Forming other types of devices suchas electrical and/or mechanical devices, including sensor arrays, isalso useful.

Referring to FIG. 2, a substrate 201 is provided on which the activecomponents of the device are formed. The substrate comprises a plasticor a polymeric material. In one embodiment, the substrate comprises aflexible substrate, such as poly(ethylene terephthalate) (PET) orpolyester for forming flexible devices. The substrate can comprise atransparent substrate to serve as, for example, a display surface for anOLED display. The use of a flexible transparent substrate for forming aflexible display is also useful. Various types of plastic substrates,such as PET, poly(butylene terephthalate) (PBT), poly(enthylenenaphthalate) (PEN), Polycarbonate (PC), polyimides (PI), polysulfones(PSO), and poly(p-phenylene ether sulfone) (PES) are useful. Othersubstrates comprising polyethylene (PE), polypropylene (PP), poly(vinylchloride) (PVC), polystyrene (PS) and poly(methyl methyleacrylate)(PMMA), can also be used.

In one embodiment, the substrate should be thin to result in a thindevice while providing sufficient mechanical integrity during thefabrication process to support the active components. Preferably, thesubstrate should be as thin as possible while providing sufficientmechanical integrity during the fabrication process. The substratethickness is, for example, about 20-200 μm. Thicker substrates are alsouseful. For example, thicker substrate, can be used where devicethickness or flexibility is not an issue.

A device layer 210 is formed on the substrate. The device layercomprises, for example, a conductive layer. Other types of devicelayers, such as dielectrics or semiconductors, are also useful. In oneembodiment the device layer comprises a transparent conductive layerthat serves as an electrode for an LED device. The transparentconductive layer comprises an indium-tin-oxide (ITO). ITO is useful informing the transparent anode of the LED device. Other transparentconductive layers, including zinc-oxide or indium-zinc-oxide are alsouseful. Various techniques, such as sputtering, physical vapordeposition (PVD), chemical vapor deposition (CVD) or plasma enhanced CVD(PECVD) can be employed to form the device layer. The device layer isdeposited on the substrate to a thickness of about, for example, 100 nm.The thickness, of course, can vary depending on design requirements.

A stamp 280 comprising a desired pattern on a surface 231 is provided.The pattern is defined by protrusion 285 on surface 231. The stamp ismade of a hard material such as steel, silicon, or ceramic. Othermaterials that are sufficiently hard can also be used to form the stamp.

In one embodiment, the pattern is deeper than the thickness of thedevice layer. This ensures proper patterning of the device layer.However, the height of the protrusions should be less than that whichwould compromise the support function of the substrate. In oneembodiment, the height of the protrusions is at least about 2-10 timesthe thickness of the device layer, preferably 5-10 times the thicknessof the device layer. For example, the height of the protrusions is about0.5-1 μm for a 100 mm thick device layer. The height of the protrusionscan be optimized according to the mechanical properties and thickness ofthe substrate.

Referring to FIG. 3, a load is applied on the stamp 280, forcing thestamp against the substrate 201. This causes the pattern on the stamp tobe transferred to the substrate. The load applied on the stamp issufficient to prevent the device layer 210 from cracking in the activeor non-patterned areas as it is patterned. In one embodiment, the netpressure of the load is about 200-400 MPa for a typical polymersubstrate. In general, the required net pressure should exceed about 1.1times the yield strength of the substrate material.

Referring to FIG. 4, the stamp is lifted from the substrate. As shown,the pattern on the stamp is transferred onto the device layer. In oneembodiment, the device layer is patterned to form electrode strips onthe substrate. Conventional processing continues to form the device.

In one embodiment, the process continues to fabricate OLED pixels of anOLED device. Fabrication of OLED pixels is described in, for example,U.S. Pat. No. 4,720,432 and Burroughes et al, Nature 347 (1990) 539,which are herein incorporated by reference for all purposes. Thisincludes, for example, depositing one or more organic functional layers,such as conjugated polymer or Alq₃, on the electrode. Other types oforganic layers can also be useful. Preferably, a plurality of functionallayers is formed on the electrode. Second electrode strips comprisingmetal such as aluminum or other conductive material are formed over thefunctional layer. The second electrode strips are typically orthogonalto the bottom electrode strips. Providing second electrode strips thatare diagonal to the bottom electrode strips is also useful. Theintersections of the top and bottom electrode strips form OLED pixels.Various techniques can be used to form the electrode strips. Forexample, the second electrode strips can be formed by selectivedeposition techniques. Alternatively, the electrode strip can be formedby selectively patterning a top electrode layer to form the strips.

In an alternative embodiment, the pattern on the stamp can be formed toinclude a plurality of devices for parallel processing, therebydecreasing process time per device. The stamp pattern can be formed by avariety of techniques. Such techniques include, for example, grinding orphotolithographic and etch processes.

FIG. 5 shows another embodiment of the invention. As shown, a stampcomprising a drum 580 with the desired pattern 585 thereon is provided.The drum stamp is used in reel-to-reel processing. A long flexiblesubstrate 501 with a device layer 510 formed thereon is provided. Thesubstrate is translated through the drum while it is pressed underrotation, patterning the device layer. As shown, the substrate istranslated in a direction from right to left and the drum stamp isrotated in the clockwise direction. Reversing the direction that thesubstrate is translated is also useful. Reel-to-reel processing enablesparallel processing of devices.

While the invention has been particularly shown and described withreference to various embodiments, it will be recognized by those skilledin the art that modifications and changes may be made to the presentinvention without departing from the spirit and scope thereof. The scopeof the invention should therefore be determined not with reference tothe above description but with reference to the appended claims alongwith their full scope of equivalents.

What is claimed is:
 1. In the fabrication of a device, a method ofpatterning a device layer comprising: providing a substrate comprisingthe device layer on its surface; and patterning the device layer bypressing a stamp comprising a pattern against the substrate and thedevice layer, wherein the pattern includes protrusions on a surface ofthe stamp, the protrusions having a height greater than a thickness ofthe device layer, wherein the protrusions directly pattern the devicelayer; wherein the patterned device layer is a part of the fabricateddevice.
 2. In the fabrication of a device, a method of patterning adevice layer comprising: providing a substrate comprising the devicelayer on its surface; and patterning the device layer by pressing astamp comprising a pattern against the substrate, wherein the patternincludes protrusions on a surface of the stamp, the protrusions having aheight that is greater than a thickness of the device layer; wherein thedevice comprises an organic LED device.
 3. The method of claim 2 whereinthe substrate comprises a polymeric substrate.
 4. The method of claim 3wherein the substrate comprises a flexible or ductile substrate.
 5. Amethod of pattering a device, comprising: providing a transparentsubstrate, wherein the substrate has a device layer on its surface; andpatterning the device layer by pressing a stamp comprising a patternagainst the substrate, wherein the pattern includes protrusions on asurface of the stamp, the protrusions having a height that is greaterthan a thickness of the device layer; wherein the device comprises anorganic LED device.
 6. The method of claim 5 wherein the device layercomprises a transparent conductive layer.
 7. The method of claim 6wherein the transparent conductive layer comprises a conductive oxide.8. The method of claim 7 wherein the conductive oxide comprisesindium-tin-oxide.
 9. The method of claim 8 wherein patterning the devicelayer forms lower electrodes on the substrate.
 10. The method of claim 9wherein the height of the protrusions is at least about 2-10 timesgreater than the thickness of the device layer.
 11. The method of claim10 wherein the stamp is pressed against the substrate under a loadwithout causing the device layer to crack in non-patterned areas. 12.The method of claim 11 wherein the load comprises a net pressure ofgreater than about 1.1 times a yield strength of the substrate.
 13. Themethod of claim 12 further comprising processing to form OLED pixels.14. The method of claim 13 wherein the processing to form OLED pixelscomprises: forming at least one organic functional layer on the lowerelectrodes; and forming upper electrodes on the organic functionallayer, wherein the OLED pixels are formed where the upper and lowerelectrodes sandwich the organic functional layer.
 15. The method ofclaim 3 wherein the substrate comprises a transparent substrate.
 16. Themethod of claim 15 wherein the device layer comprises a transparentconductive layer.
 17. The method of claim 16 wherein patterning thedevice layer forms lower electrodes on the substrate.
 18. The method ofclaim 17 wherein the stamp is pressed against the substrate under a loadwithout causing the device layer to crack in non-patterned areas. 19.The method of claim 18 further comprising processing to form OLEDpixels.
 20. The method of claim 19 wherein the processing to form OLEDpixels comprises: forming at least one organic functional layer on thelower electrodes; and forming upper electrodes on the organic functionallayer, wherein the OLED pixels are formed where the upper and lowerelectrodes sandwich the organic functional layer.
 21. The method ofclaim 3 wherein the device layer comprises a conductive layer.
 22. Amethod of patterning a device layer, comprising: providing a polymericsubstrate comprising a device layer on its surface, wherein the devicelayer comprises a conductive layer; and patterning the device layer bypressing a stamp comprising a pattern against the substrate, wherein thepattern includes protrusions on a surface of the stamp, the protrusionshaving a height that is greater than a thickness of the device layer,wherein the patterning forms lower electrodes on the substrate; whereinthe device comprises an organic LED device.
 23. The method of claim 22,wherein the stamp is pressed against the substrate under a load withoutcausing the device layer to crack in non-pattered areas.
 24. The methodof claim 23 further comprising processing to form OLED pixels.
 25. Themethod of claim 24 wherein the processing to form OLED pixels comprises:forming at least one organic functional layer on the lower electrodes;and forming upper electrodes on the organic functional layer, whereinthe OLED pixels are formed where the upper and lower electrodes sandwichthe organic functional layer.
 26. The method of claim 2 wherein thesubstrate comprises a material selected from the group consisting ofpolyester, poly(ethylene terephthalate), poly(butylene terephthalate),poly(enthylene naphthalate), polyethylenesterephtalate, polycarbonate,polyimides, polysulfones, poly(p-phenylene ether sulfone), polyethylene,polypropylene, poly(vinyl chloride), polystyrene, and poly(methylmethyleacrylate).
 27. The method of claim 26 wherein the device layercomprises a conductive layer.
 28. The method of claim 27 wherein thepattern is used to form lower electrodes on the substrate.
 29. Themethod of claim 28, wherein the stamp is pressed against the substrateunder a load without causing the device layer to crack in non-patternedareas.
 30. The method of claim 29 further comprising processing to formOLED pixels, the method further comprising: forming at least one organicfunctional layer on the lower electrodes; and forming upper electrodeson the organic functional layer, wherein OLED pixels are formed wherethe upper and lower electrodes sandwich the organic functional layer.31. The method of claim 1 wherein the substrate comprises a polymericsubstrate.
 32. The method of claim 31 wherein the height of theprotrusions is at least about 5-10 times greater than the thickness ofthe device layer.
 33. The method of claim 32 wherein the stamp ispressed against the substrate under a load without causing the devicelayer to crack in non-patterned areas.
 34. The method of claim 33wherein the load comprises a net pressure of greater than about 1.1times a yield strength of the substrate.
 35. The method of claim 34further comprising processing to form the device.
 36. The method ofclaim 35 wherein the device comprises a device selected from the groupconsisting of an electrical device, a mechanical device, aelectromechanical device, and a microelectromechanical system.
 37. Themethod of claim 31 wherein the stamp is pressed against the substratesurface under a load without causing the device layer to crack innon-patterned areas.
 38. The method of claim 37 further comprisesprocessing to form the device.
 39. The method of claim 37 wherein thedevice comprises a device selected from the group consisting of anelectrical device, a mechanical device, a electromechanical device, anda microelectromechanical system.
 40. The method of claim 1 wherein thesubstrate comprises a material selected from the group consisting ofpolyester, poly(ethylene terephthalate), poly(butylene terephthalate),poly(enthylene naphthalate), polyethylenesterephtalate, polycarbonate,polyimides, polysulfones, poly(p-phenylene ether sulfone), polyethylene,polypropylene, poly (vinyl chloride), polystyrene, and poly(methylmethyleacrylate).
 41. The method of claim 40 wherein the stamp ispressed against the substrate under a load without causing the devicelayer to crack in non-patterned areas.
 42. The method of claim 41further comprising processing to form the device.
 43. A method ofpatterning a device layer in the fabrication of a device, comprising:rotating a stamp comprising a drum with a pattern; and translating asubstrate with a device layer thereon as the stamp is rotated todirectly pattern the device layer; wherein the patterned device layer isa part of the fabricated device.
 44. The method of claim 43 wherein thesubstrate comprises a polymeric substrate.
 45. The method of claim 44wherein the pattern is produced by protrusions on a surface of thestamp.
 46. The method of claim 45 wherein the protrusions comprise aheight greater than a thickness of the device layer to pattern thedevice layer.
 47. The method of claim 46 wherein the stamp is pressedagainst the substrate under a load without causing the device layer tocrack in on non-patterned areas.
 48. The method of claim 47 furthercomprising processing to form the device.
 49. The method of claim 48wherein the device comprises a device selected from the group consistingof an electrical device, a mechanical device, a electromechanicaldevice, and a microelectromechanical system.
 50. The method of claim 48wherein the device comprises an OLED device.
 51. The method of claim 43,wherein: translating a substrate includes separating the device layerinto a first portion and a second portion; the first portion contactsprotruding portions of the pattern during the step of translating thesubstrate; and the first portion does not contact the second portionafter the step of translating the substrate.
 52. The method of claim 1,wherein: patterning the device layer includes separating the devicelayer into a first portion and a second portion; the first portioncontacts protrusions of the pattern during the step of patterning thedevice layer; and the first portion does not contact the second portionafter the step of patterning the device layer.
 53. The method of claim2, wherein: patterning the device layer includes separating the devicelayer into a first portion and a second portion; the first portioncontacts the protrusions of the pattern during the step of patterningthe device layer; and the first portion does not contact the secondportion after the step of patterning the device layer.